The present invention relates to a method for forming a golf ball and relates to a mold used therefore.
As a method for producing a golf ball, Japanese Patent No. 3319708 discloses a method, as a conventional technique, in which in providing a layer, an inner core located more to the inside of the ball than the layer, is separately molded by vulcanization, then the inner core is fixed at a predetermined location within a mold by means of a movable holding pin, then a material for forming an outer layer is injection-molded by using an injection molding machine or a transfer mold, and the holding pin is withdrawn at an appropriate timing, and vulcanization molding is performed in this state. In order to avoid increase in cost due to complicated processes and mold structure required in such a molding method that uses a pin, Japanese Patent No. 3319708 discloses a method for forming a golf ball having an outer layer and an inner layer which does not use a holding pin, in which an unvulcanized material is semi-vulcanized to form a hemispherical shell-like outer layer half split bodies and then an unvulcanized material for forming the inner layer is sandwiched between a pair of the above-described semi-vulcanized outer layer half split bodies to press-mold the same by vulcanization.
In addition, Japanese Patent No. 3663580 discusses a method for producing a golf ball, in which an unvulcanized material is semi-vulcanized or vulcanized to form hemispherical shell-like outer layer half split bodies, and then an unvulcanized material for forming an inner layer is sandwiched between a pair of the above-described outer layer half split bodies to form a golf ball including the outer layer and the inner layer, and the inner layer forming material is poured between the outer layer half split bodies to at the same time form an invaded portion formed by the inner layer passing through or engaged in at least a part of a seam portion of the outer layer, in which the volume of the passing or engaged invaded portion is 1/300 to ⅕ of a volume considered to be obtained if it is assumed that the outer layer has the shape of a complete spherical shell.
Japanese Patent No. 4019242 discusses a method for producing a multilayered golf ball having a core covered with at least outermost layer covers and an intermediate layer cover sandwiched therebetween, in which a top/bottom split mold is used, a core or a sphere covered with the intermediate cover is provided inside the mold, a cover material is injection-molded around the core or the sphere, the cover material is molded so that the molded body has a spherical shape and a thickness of 1.1 mm or more, and then the surface of the sphere-like molded body is cut and processed to leave a cutting margin of 0.3 to 2 mm to obtain a sphere of which the product thickness of the above-described intermediate layer cover or the outermost layer cover is 1 mm or less.